This invention relates to a device for fixing an image under pressure on a recording medium, used in connection with electronic copiers, printers, facsimiles, and the like.
With such copying and printing machines, an image of a manuscript is electrostatically or electromagnetically formed on a sheet-shaped recording medium as a toner image or formed as a latent image on a recording medium carrying a plurality of photo-sensitive microcapsules each containing color ink or the like by exposing an optical image thereon. The image thus formed is then fixed or developed on the same or a separate recording medium with an image fixing device which applies constant pressure uniformly over the entire surface of the recording medium to fix or develop the image.
One example of the image fixing device is disclosed in Japanese Patent Provisional Publication No. SHO57-185067, in which a lower support roller and an upper press roller are opposedly arranged and brought into contact with each other to provide a predetermined contact pressure therebetween. A recording medium on which a toner or latent image has been formed is adapted to pass between these rollers so that said predetermined pressure is applied to the surface of the recording medium to fix or develop the toner or latent image.
With the said prior art device, however, since the upper press roller contacts with the lower support roller over the entire width thereof, there is required an extremely great contact pressure in order to provide substantially uniform pressure all over the entire surface of the recording medium. To meet this requirement, it would be necessary to strengthen shafts of these contact rollers and a frame for supporting the rollers, resulting in considerable increase of the size and a manufacturing cost of the device. Meanwhile, fixing or developing quality will be degraded if pressure is not applied uniformly over the entire surface of the recording medium.